This invention relates to a rear projection screen and a manufacturing method therefor on which screen an image is made visible for viewing on the front surface side by being projected from the rear surface side, to a molding die for shaping rear projection screens which is suitable to manufacture the rear projection screen concerned, and to an overhead projector and a projection television set serving as a projection system which is equipped with the rear projection screen concerned.
Heretofore, there has already been known the rear projection screen on which an image projected from the rear surface side is made visible for viewing from the front surface side, and it is the real state that various types of rear projection screens have been proposed. In recent years, particularly, it is necessary for color televisions that the rear projection screen to be used in adding different images of primary colors consisting of red, green and blue on the picture must be a screen of the special configuration unlike the screen of a color slide projector or of a motion picture projector which is to be used in projecting a multicolored image itself.
By the way, examples of the rear projection screen which is to be used in adding on the picture the different images of the primary colors consisting of red, green and blue as in the case of the color television are disclosed in Japanese Patent Unexamined Publication Nos. 58-216234 and 58-216235, for example. In these screens, a plurality of convex lenses are arranged on one side so as to form a first lens surface, another plurality of convex lenses are installed on the other side in such a manner that the optical axis of these lenses coincides with that of the convex lenses of the first lens surface, so as to form a second lens surface, and a light screening layer is installed to convex parts in the non-condensing part of the convex lenses of the first lens surface which are projected forward from the second lens surface.
However, the above-described publications have problems of practical application, although there are described about the material and the manufacturing method of the screen. Namely, it is difficult to manufacture the screen, and therefore, it is impossible to easily obtain the screen at low cost.